The quality of the eye's sensory function greatly depends on the qualities of light conduction through the cornea and through the lens, and also the optical qualities of these organs and the transparency of the cornea and the eye lens, as well as other factors.
Experts in the field of ophthalmology know that corneal transparency generally depends on the ability of the cornea to remain in a dehydrated state. The cornea dehydrated state is affected by several interdependent factors, the most important of which is an active pump present in the deepest cell layer of the cornea, the endothelium. Any disruption of the endothelial function beyond a certain level as a result of surgery, trauma, infection, or congenital predisposition results in influx of water to all layers of the cornea thus distorting its transparency. The morbidity of this situation is not only a significant decrease in vision, but also at an advanced state may result in significant pain and scars, a situation known as bullous keratopathy.
Another important physiological mechanism for dehydrating the cornea is the evaporation of water from the tear film while the eye is open during wakefulness. Dehydration works by water evaporating from the tear film, which leaves behind a more concentrated solution at the surface of the eye, causing the tear film to be more hypertonic. The hypertonic tear film draws more water by osmosis from the cornea itself; the opposite is true during the night. There are some hypertonic solution eye drops available in the market to augment this mechanism but unfortunately their action is short lived due to the blinking of the eyelids.
Currently, there is no conservative treatment for an unhealthy edematous state. Several surgical procedures have evolved to address this problem: from the classical full thickness corneal transplantation to more recently developed surgical procedure called deep lamellar striping keratoplasty (DLEK) and Descemets striping endothelial keratoplasty (DSEK). In the later, a thin posterior or lenticule of stromal tissue (along with Descemet's membrane and endothelial cells attached) is removed from the cornea of a diseased eye. A similar procedure is performed on a donor eye to obtain donor tissue. When the donor tissue is placed in the recipient's eye, no sutures are required to hold the graft to the host cornea. All of these procedures have the disadvantage of being donor dependent.